1. Field of the Invention
The present invention relates to a ranging and positioning system, a ranging and positioning method, and a radio communication apparatus for measurement of a relative distance between two objects, and particularly to a ranging and positioning system, a ranging and positioning method, and a radio communication apparatus for measurement of a relative distance between two objects by means of radio waves.
More particularly, the present invention relates to a ranging and positioning system, a ranging and positioning method, and a radio communication apparatus for measurement of a relative distance between two radio sets which transmit and receive packets to and from each other, and specifically to a ranging and positioning system, a ranging and positioning method, and a radio communication apparatus for ranging and positioning by means of the procedure for packet transmission and reception between a sender and a recipient.
2. Description of the Related Art
There has existed for a long time the ranging and positioning system relying on radio waves, which is exemplified by the radar which utilizes reflection of radio waves or the radio navigation system which employs more than one reference station.
Loran and GPS (Global Positioning System) are capable of positioning with the help of radio equipment which simply receives signals, because reference stations are strictly synchronized with one another.
Other positioning methods than Loran and GPS include the one which uses radio waves from base stations for portable telephones (patent literature 1) and the one which uses radio waves for television (non-patent literature 1 and patent literature 2). They are basically the same although the latter makes corrections according to data received from a separate base station in order to monitor deviation from synchronization because it lacks strict synchronization.
Vehicular communications by ITS (intelligent transport system) employ a ranging system called “Boomerang System” to measure the distance between motor vehicles. This system does not require radio sets to be synchronized with each other. It performs ranging in the following manner, for example. A radio set which wants to perform ranging transmits signals. The other radio set, which is an object for ranging, receives the signals and sends them back together with its own information superimposed thereon. The first radio set to perform ranging measures the time required for radio waves to go and come back. In this way it achieves its objective.
According to the above-mentioned method, the radio set as an object for ranging simply returns the received signals without further processing. There is another system to estimate distances from the period of time taken from transmission of signals by the radio set which wants to measure distance to reception of returned signals by the radio set as an object for ranging. The period of time includes the signal processing time taken by both of the radio sets. (patent literature 3).
There has recently been developed a new radio communication system called “ultra-wide band (UWB) communication”. It performs radio communication by superimposing information on a train of extremely weak impulses. Its practical use is expected for short distance transmission at ultra-high speeds. (non-patent literature 2).
The UWB transmission system falls into two categories. The first one is “DS-UWB system” in which the rate of spreading of DS information signals is increased to extremes. The second one is “impulse UWB system” in which information signals to be transmitted and received are constructed of a train of impulses having a very short period (say, some hundreds of picoseconds). Both systems employ extremely spread frequency bands (from 3 to 10 GHz) to transmit and receive signals, thereby achieving high-speed data transmission. They have an occupied band width (of the order of gigahertz) such that the quotient of the occupied band width divided by the center frequency (say, 1 to 20 GHz) is approximately 1. Thus, their band width is much broader than those which are usually used for wireless LAN based on W-CDMA system, cdma 2000 system, SS (spread spectrum) system, or OFDM (orthogonal frequency division multiplexing) system.
The UWB communication system employs extremely short pulses and hence has a high time resolution. With the help of this characteristic, it can perform ranging and positioning. The recent UWB communication system can perform ranging in addition to high-speed data transmission in excess of 100 Mbps.
WPAN (wireless personal access network) for short distance communications, which is typified by UWB, is expected to be installed in every domestic appliance and consumer electronics equipment. Consequently, it is expected to find new uses such as navigation and NFC (near field communications) which rely on position information obtained from ranging. This adds a new value to radio communication. The future radio equipment for high-speed data transmission should desirably be provided also with the ranging function.
As mentioned above, ranging is usually accomplished by measuring the time taken from packet transmission to packet reception. Keeping this time fixed is inconvenient to the system whose processing varies depending on the length and kind of packets. Moreover, adding special information for ranging to packets is not desirable in view of the effective use of band width.
Patent literature 1:
Japanese Patent Laid-open No. 257545/1998
Patent literature 2:
Japanese Patent Laid-open No. 119145/1993
Patent literature 3:
Japanese Patent Laid-open No. 62334/1996
Non-patent literature 1:
http://www.rosum.com
Non-patent literature 2:
Nikkei Electronics, Mar. 11, 2002, p. 55-66 “Ultra Wideband: Revolutionary Wireless Technology is born”